Turbulent gas that favors star formation found in distant galaxies

An article published in the journal “Nature” describes the first detection in the distant universe of the carbon hydride molecule, or CH+. A team led by Edith Falgarone of the Ecole Normale Supérieure and Observatoire de Paris, France, used the ALMA radio telescope to discover that cold and turbulent gas in galaxies of the starburst type such as SMM J2135-0102, nicknamed Cosmic Eyelash. This discovery will help to better understand the mechanisms of galaxy growth and the periods of rapid star formation.

Starburst galaxies are characterized by a star formation rate much higher than galaxies like the Milky Way. For this characteristic, they’re considered ideal to study the growth and interaction between gas, dust and the supermassive black hole at their center. For this reason, 6 galaxies of this type were examined using the ALMA (Atacama Large Millimeter/submillimeter Array) radio telescope, inaugurated in March 2013, and in 5 of them the CH+ molecule was found.

The discovery in the space of this molecule, an ion of the CH molecule, is not new since it was one of the first molecules discovered in interstellar space in the 1940s. However, for decades its presence has been a mystery because CH+ is extremely reactive and therefore it combines with other molecules more quickly than others. Another characteristic of CH+ is that it takes a lot of energy to form so it’s useful to trace the energy flows within galaxies and their surroundings.

An analogy is that of a boat on a tropical ocean in a dark moonless night: when the conditions are right, the fluorescent plankton lights up around the boat while it’s moving. The turbulence caused by the boat slipping on the water stimulates the plankton to emit light that reveals the existence of dark turbulent regions underwater. CH+ is formed only in small areas where the turbulent gas motions dissipate therefore its detection essentially traces energy on a galactic scale.

The connection to star formation is derived from the CH+ observations that reveal dense shock waves, powered by hot and fast galactic winds originated in star-forming regions within the galaxy. The flow of these winds passes through a galaxy and pushes the material outward but their turbulent winds are such that some of the materials can be recaptured by the force of gravity of the galaxy itself (up left in the bottom image).

This material is collected in a large turbulent reservoir of cold low-density gas that extends for more than 30,000 light-years away from the galaxy’s star formation region. Such reservoirs could be of the same nature as the gas halos discovered around quasars described in a research published in the journal “The Astrophysical Journal” in October 2016.

However, the cold gas reservoirs that can surround a galaxy weren’t known and were detected thanks to the CH+ molecule detection. The turbulence in the reservoirs generates galactic winds that extend the phase of intense star formation rather than suppress it and this contradicts the current models of galaxy formation and evolution.

According to the researchers, those galactic winds alone are not enough to fill up of gas the reservoirs they discovered so it’s possible that more gas is supplied in galactic mergers or by hidden gas flows and that’s predicted by the current models. In essence, the situation that was discovered in those galaxies is partially new so the research was fruitful.

This discovery could be a significant step forward in understanding the mechanisms that regulate the flow of materials in starburst galaxies in the earlt universe. The use of the very powerful ALMA radio telescope was exploited by scientists from various disciplines who combined their knowledge to achieve this progress.